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18650 vs 21700 battery packs.

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  • Retrorockit
    replied
    i found this site having a Black Friday 50% off sale on some of their 21700 stufff. I'll just link to the thread here.
    This is a new Ebay vendor. Seems to be associated with Hailong. Ships from a US warehouse. I haven't used them yet. The 21700 batteries are Panasonic. the others are not so specific. 50% off sale. https://webmail1.earthlink.net/folders/INBOX/messages/214164

    Leave a comment:


  • stts
    commented on 's reply
    I think I will end up going the 21700 route. Lifepo4 is just too big and costs too much. And the used battery deals that are remotely workable are for 7 year old batteries. That is just too crazy to be selling batteries that old. Ill just have to think about a safe place outside to keep my battery. Like in the grill, hah.

  • Retrorockit
    replied
    There is a tropical storm moving in. Lots of headwinds. 20mph and gusting 25-30mph. I decided to take my longer 36mile ride and see what happened. Went out and 1/2 way back. Sat out the first rain squall at my favorite Irish pub. Finished the ride in a light drizzle. Skipped my 30 mph runs at the end. Not needed due to light traffic. Got home with a flat battery but still PAS 1 powered, I did this as a battery test. The test was a success and so was the battery. I thought I might have more than this left, but it wasn't dead and I WAS trying to stress it. PAS 3 and 4/5 into the wind where normally I'm PAS2
    This is probably my last ride for the next few days. This is expected to be a hurricane when it lands a little north of where I am. I'm on the soft side of it, so not too worried.

    Leave a comment:


  • Retrorockit
    commented on 's reply
    I guess this is how I got there.
    ​​​​​​​https://www.greenway-battery.com/new...tery-1959.html

  • Retrorockit
    commented on 's reply
    It's often followed by rain.
    I suppose this thread could be considered as being about the pros and cons of getting a 24Ah battery. 21700 cells are just how I came to own one.
    It's a very nice thing to have for me, and might give an extra years useful life making it cost effective. Time will tell.
    Last edited by Retrorockit; 11-03-2022, 09:53 AM.

  • AZguy
    commented on 's reply
    Strong wind sux

    Enough said lol

  • Retrorockit
    commented on 's reply
    I'm on normal sized 35psi street tires and paved roads. I can make the theoretical numbers if there is no wind and I don't make 30+mph runs every now and then.
    Before I wouldn't raise the assist level for headwinds, just ride slower and pedal harder to make my miles. Now I just turn up the assist to maintain my normal speed. I'm not necessarily doing less work, just fewer compromises.Almost none actually.
    A ride to the beach can involve riding on busy road into a 20mph headwind all the way @ 25mph. PAS4/5. 24Ah comes in handy then. So does the BBSHD
    Last edited by Retrorockit; 11-03-2022, 07:44 AM.

  • AZguy
    commented on 's reply
    FWIW the range of Wh/mi that I've gotten through the entire life of my electric bike riding is a high of 25.9 (It's very unusual for me to exceed 20) and a low of 6.8... typically I'm in the 12-17 range, likely about 90% of my rides are in that... 20Wh/mi would be a very safe and conservative budget for me and frankly I could count on a lot less just by riding style...

    Clearly, YMMV ;-}

  • Retrorockit
    replied
    I saw your formula for range Wh/20=Miles. So here it is 48V.x24Ah=1152Wh/20=57.6 miles.
    So a 45 mile ride with headwinds and an occasional top speed run are all in a days work.
    My original 18650 battery 48Vx17.5Ah=840Wh/20=42miles. Obviously some compromises would have to be made along the way.
    30 mile range was realistic for my conditions.
    3 year old battery 48Vx12Ah=576Wh/20=28.8 miles.
    In my world a 22 mile ride to lunch and back was about it towards the end.
    Last edited by Retrorockit; 11-03-2022, 07:23 AM.

    Leave a comment:


  • calfee20
    commented on 's reply
    2170's are available inside Dewalt 6 amp Batteries. I bought a stupid amount of them. Maybe I will start to work on them if I can get my other million projects done.

  • Retrorockit
    commented on 's reply
    It looks like no one in the US wants to offer a 48V 24Ah,40A. Mega Shark 21700 battery any more. The guy listed above stops at 20Ah. I doubt if I have the only one, but it's the only one I've seen for sale. The 21700 really comes into it's own at the end of a long ride.Especially if I've been fighting 20mph headwinds both ways.
    Nothing wrong with my old 17.5Ah 18650 battery when new. But 3 years old it was maybe 12Ah.and probably not making it's whole 30A either, or not for long anyway. If after 3 years this is still making 16Ah and 30A I'll be real happy.
    Last edited by Retrorockit; 11-03-2022, 05:51 AM.

  • AZguy
    commented on 's reply
    Engineering isn't about exact, it's about being close enough
    Last edited by AZguy; 11-02-2022, 04:37 PM.

  • stts
    commented on 's reply
    I cant agree with you at all. Its totally voodoo. A lawsuit defense from fraud citing an "average" from 58 volts will be shot down in flames. And a failed grade in any engineering class. And a spacecraft that misses mars landings by planetary units. The graph of battery discharge voltage that I have seen posted here many times shows an exponential drop from initial voltage right from the start. You cant average in exponential components to a linear equation. Averages only apply to linear processes. Watts law is just dead on. Bet on it and collect in vegas. :)

    A 52 volt battery is indeed a better battery than a 48v battery. At 20Ah its 1040Wh as opposed to 960Wh. If the controller can be set for 52v, then the controller will have 80 more watts of power to use. The advantage of higher voltage is the lowering of the current to deliver the same power. Lower current means lower heat losses and more of the power is used to go more miles. Thats why cars use very high DC voltages. 48volts in a car would just cook everything inside in short order. So fork lift systems are never used in cars.
    Last edited by stts; 11-02-2022, 01:22 PM.

  • AZguy
    commented on 's reply
    Hardly voodoo

    Dividing the sum of the initial voltage and the final voltage by two gets the average of the two so is a suitable approach to calculating energy capacity - and as explained if the discharge voltage was linear, entirely accurate

    OTOH the accepted approach is to use the nominal cell voltage (3.7V) as I did in the latter example

    The difference between the two methods for a 52V 20Ah battery would give the 974Wh as explained and if using the nominal cell voltage (optimistic since it would require running the battery to 0% which nobody does) would give 1036Wh - very close and higher as expected



    But again, the *only* way to know what the capacity is (usable or total), is to measure it with a Wh/Ah coulomb counting meter

  • stts
    commented on 's reply
    Yup jyouellette got it all wrong. But AZ used that equation divided by 2 as well. Total Voodoo science. Watts law is undisputeable. And things run very well by it. The battery actual usefull power when new is legally 960Wh when stamped with a label of 20Ah. No question. The battery WILL by law put out all that power. But its not the battries fault what is done with that power. If its used to haul an elephant, it will be lucky if that power buys a mile of travel. If its used to haul canaries, and you can keep half of them flying, well, that battery is definitely going places. :)
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